In release-10 of LTE (Long Term Evolution), “Intra-eNB CA (Carrier Aggregation)” in which multiple CCs (Component Carriers) under the same radio base station eNB are aggregated to perform communication as shown in part (a) of FIG. 5 has been introduced to achieve communication in a wide bandwidth exceeding 20 MHz (for example, communication of 100 MHz).
Later, Release-12 and beyond of LTE have proposed “Small Cell Enhancement”, and “Inter-site CA” in which communication is performed by aggregating CCs (cells) under different radio base stations eNB has been considered to be introduced as one of network architectures which are more flexible than conventional architectures (see part (b) of FIG. 5).
For example, the following operation is conceivable by using the “Inter-site CA”. As shown in part (b) of FIG. 5, a C-plain signal for which reliability needs to be secured is communicated through a SRB (Signaling Radio Bearer) in a cell #1 (macro cell) under a radio base station eNB#1 (macro eNB), and a U-plane signal which requires broadband communication is communicated through a DRB (Data Radio Bearer) in a cell #10 (small cell) under a radio base station eNB#10 (small radio base station).